US11906685B2 - Distinguishing false signals in cable locating - Google Patents
Distinguishing false signals in cable locating Download PDFInfo
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- US11906685B2 US11906685B2 US17/157,106 US202117157106A US11906685B2 US 11906685 B2 US11906685 B2 US 11906685B2 US 202117157106 A US202117157106 A US 202117157106A US 11906685 B2 US11906685 B2 US 11906685B2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/12—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with electromagnetic waves
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/15—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for use during transport, e.g. by a person, vehicle or boat
- G01V3/165—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for use during transport, e.g. by a person, vehicle or boat operating with magnetic or electric fields produced or modified by the object or by the detecting device
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/15—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for use during transport, e.g. by a person, vehicle or boat
- G01V3/17—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for use during transport, e.g. by a person, vehicle or boat operating with electromagnetic waves
Definitions
- the present invention relates generally to a system and method for locating buried lines such as, for example, pipes, cables, conduits or other conductors and, more particularly, to a locating arrangement that is configured for distinguishing “false” cable locating signals.
- the prior art has been limited by at least one aspect of the aforedescribed technique.
- the electromagnetic signal that is transmitted from a particular cable of interest can be coupled to another cable in the region. This coupling can take place through the ground or can occur when the cables are in physical contact, for example, at their distal ends whereby a direct, resistance-type electrical connection is formed between the cables.
- the locating signal is coupled to another cable, that cable will re-emit the locating signal.
- the re-emitted locating signal is, in most cases, indistinguishable from the original locating signal.
- the present invention resolves the foregoing limitations in a highly advantageous way, while providing still further advantages, as will be described immediately hereinafter.
- a system and method are described for discriminating between the locating signal and the false locating signal.
- a reference signal which contains the locating signal frequency impressed thereon, is transmitted in a way which provides for detection of a phase shift between the locating signal and the false locating signal. Based on the phase shift, a receiver is used to distinguish the locating signal from the false locating signal.
- the locating signal is electromagnetically coupled from the first cable to the second cable through the ground to cause the second cable to emit the false locating signal.
- the locating signal frequency is recovered from the reference signal. Synchronous detection of the locating signal frequency and a selected frequency band, which includes said locating signal and said false locating signal, is performed in a way which substantially rejects the false locating signal while providing an output responsive to the locating signal.
- FIG. 1 is a diagrammatic elevational view of a region in which the cable locating system and method of the present invention are operating including two cables disposed in the region, one of which transmits the locating signal of interest and the other of which transmits a false, potentially interfering signal.
- FIG. 2 is a diagrammatic plan view of the region of FIG. 1 including the cables disposed therein along with the system of the present invention.
- FIG. 3 is a diagrammatic plan view of the region in which the cable locating system and method of the present invention are operating including two cables that are resistively connected at distal ends thereof.
- FIG. 4 is a block diagram which illustrates one embodiment of a transmitter produced in accordance with the present invention.
- FIG. 5 is a diagrammatic see-through view, in perspective, which illustrates one embodiment of a locator/receiver that is produced in accordance with the present invention.
- FIG. 6 is a diagrammatic see-through view, in perspective, which illustrates another embodiment of a locator/receiver of the present invention including a dependent wand which houses an additional antenna arrangement.
- FIG. 7 is a block diagram which illustrates one embodiment of a receiver that may be used in a portable locator in accordance with the present invention.
- FIG. 8 is a block diagram which illustrates another embodiment of a transmitter, produced in accordance with the present invention, including selective cable locating signal connection capabilities.
- FIG. 9 is a block diagram which illustrates still another embodiment of a transmitter, produced in accordance with the present invention, that is capable of transmitting a reference signal using an RF carrier.
- FIG. 10 is a block diagram which illustrates another embodiment of a receiver/locator of the present invention which is configured for receiving a reference signal modulated on an RF carrier.
- FIG. 11 is a diagrammatic view, in elevation, of a region in which the transmitter of FIG. 9 and the receiver of FIG. 10 are in use, shown here to illustrate further details with respect to their operation.
- Region 10 includes a first cable 12 and a second cable 14 , each of which includes an electrically conductive component which may be used for purposes of transmitting an electromagnetic locating signal, as will be further described.
- the surface of the ground is indicated by reference number 16 .
- System 100 includes a transmitter 102 and a receiver/locator 104 , as will be described in detail at appropriate points hereinafter.
- transmitter 102 generates a locating signal frequency f L and a reference signal R, and includes any suitable coupling configuration 112 for coupling the locating signal frequency or the locating frequency in combination with the reference signal onto cable 12 .
- This coupling can be accomplished using inductive coupling or a direct electrical connection, both of which are considered as familiar to one having ordinary skill in the art. It is noted that exemplary waveforms have been illustrated in FIG. 1 with respect to f L and R as well as other physical quantities of interest, as will be further described.
- this cable Having coupled the locating signal frequency and the reference signal onto cable 12 , this cable emanates a locating signal which is designated as L and a signal R′ which designates the reference signal subject to the phase shift of coupling configuration 112 .
- L locating signal
- R′ which designates the reference signal subject to the phase shift of coupling configuration 112 .
- the specific magnitude of the phase shift depends upon the specific type of arrangement that is used to couple the locating signal frequency to the cable.
- the use of inductive coupling is contemplated wherein locating signal L leads locating signal frequency f L by approximately 90°. For reasons which will be made evident below, an awareness of the phase characteristics of coupling configuration 112 is generally needed.
- locating signal L travels through the ground and can be coupled to cable 14 .
- the degree of coupling is dependent upon various factors such as, for example, proximity and resistive path from one cable to the other. A detailed discussion of these factors, however, is not necessary to an understanding of the present invention and is therefore considered to be beyond the scope of the present description.
- cable 14 under many circumstances, produces a reemitted or “false” locating signal L F . If this reemitted locating signal is viewed solely in terms of its frequency, it is indistinguishable from locating signal L.
- many operators of prior art cable locating systems may inadvertently follow cable 14 , as opposed to cable 12 .
- FIG. 3 a diagrammatic plan view of region 10 illustrates an alternative situation with respect to a first cable 12 ′ and a second cable 14 ′.
- each of these cables includes a distal end and these distal ends are electrically connected to one another by a resistance connection.
- the latter may occur deliberately, for example, in a junction box (not shown) or through inadvertent direct contact.
- the specific mechanism through which the resistance connection arises has no effect on system 10 and the use of the locating technique to be described in further detail below.
- Transmitter 102 includes a high-frequency or carrier generator 140 which may operate at any suitable frequency in view of a contemplated locating signal frequency (as illustrated in FIG. 1 ). The latter is generated by a low-frequency or locating signal frequency generator 142 .
- One useful locating signal frequency has been found to be approximately 30 kHz with a carrier generator frequency of approximately 300 kHz, although these values are not intended to be limiting.
- the locating signal frequency may be in the range of approximately 1 Hz to 80 KHz while the carrier generator frequency may be in the range of approximately 10 Hz to 300 KHz.
- it may be useful to maintain a value in of from 5 to 10 as a ratio of the carrier generator frequency to the locating signal frequency.
- no harmonic requirement need be imposed with respect to this frequency relationship.
- a modulator 144 receives the carrier generator signal from carrier frequency generator 140 , as well as the locating signal frequency from low frequency signal generator 142 .
- Modulator 144 impresses the locating signal frequency onto the carrier frequency using any suitable form of modulation such as, for example, amplitude modulation or frequency modulation.
- An output 146 of modulator 144 comprises a modulated carrier, the appearance of which depends on the specific form of modulation that is employed, as will be familiar to those having ordinary skill in the art. This modulated output may be referred to herein as a “reference” signal for reasons which will become evident below. It is noted that the reference signal corresponds to R of FIG. 1 .
- Output 146 is connected to a summer 148 .
- Locating signal generator 142 also provides its output to summer 148 .
- An output of summer 148 comprises the additive combination of the reference signal and the locating signal frequency, R+f L . This combination is then supplied to an amplifier which drives coupling configuration 112 . As described above, the latter may comprise an inductive clamp, an inductive arrangement (whereby the transmitter is simply positioned immediately adjacent to the cable), or a direct electrical connection.
- this phase shift will be approximately 90 degrees, depending upon coupling configuration 112 .
- L is shown as leading f L .
- the modulation envelope of the reference signal is unaffected, at least from a practical standpoint. That is, the modulation envelope of phase shifted reference signal R′ is essentially identical to the modulation envelope of reference signal R and the phase shift of the carrier produces only a small phase shift of the modulation envelope which would affect determinations made herein that rely on the modulation envelope.
- locating signal frequency f L is recoverable from R′ as its modulation envelope.
- Locator 104 includes a three-axis antenna cluster 202 measuring three orthogonally arranged components of magnetic flux in locator fixed coordinates.
- the antenna cluster could be composed of magnetometers which would be advantageous at lower frequencies.
- One useful antenna cluster contemplated for use herein is disclosed by U.S. Pat. No. 6,005,532 entitled ORTHOGONAL ANTENNA ARRANGEMENT AND METHOD which is commonly assigned with the present application and is incorporated herein by reference. It is noted that this antenna cluster is advantageous with respect to generating a vector sum of the local flux intensity.
- Antenna cluster 202 is connected to a receiver section 204 , which will be described in detail at an appropriate point below.
- a tilt sensor arrangement (not shown) may be provided for measuring gravitational angles from which the components of flux in a level coordinate system may be determined.
- Locator 200 further includes a graphics display 206 , a keypad 208 and a microprocessor 210 interconnected appropriately with the various components.
- a telemetry arrangement 212 having an antenna 214 is optional, under control of microprocessor 210 , and is provided based on the specific system implementation, as will be discussed at appropriate points hereinafter.
- an azimuth sensor in the form of a tri-axial magnetometer 216 to aid in position determination relative to a selected direction
- a cable orientation and ultrasonic transducers (not shown) for measuring the height of the locator above the surface of the ground.
- ultrasonic transducer arrangement is described, for example, in U.S. Pat. No. 6,232,780 which is commonly assigned with the present application and is incorporated herein by reference.
- antenna cluster 202 is oriented having a receiving axis arranged along an axis of symmetry of the locator.
- components of the received electromagnetic locating signal are designated as b x , b y , b z with b x being oriented along the axis of symmetry of the locator.
- locator 104 is useful with respect to a wide variety of cable locating techniques.
- One highly advantageous cable locating technique is described in U.S. Pat. No. 6,496,008, entitled FLUX PLANE LOCATING IN AN UNDERGROUND DRILLING SYSTEM, which is commonly owned with the present application and is incorporated herein by reference. Additional highly advantageous cable locating techniques are described in U.S.
- Locator 104 ′ is essentially identical to locator 104 with the addition of a downwardly dependent wand 250 .
- the latter includes a distal end which houses an additional antenna cluster 202 ′. Details with regard to the use of this alternative locator implementation will be provided at an appropriate point below.
- locator 104 may include items such as, for example, an operator actuatable trigger or push button switch. It is noted that this particular embodiment does not use a telemetry arrangement.
- Receiver section 204 includes a receiver and signal processing section 271 and a high frequency section 272 , connected to section 271 , having a bandpass filter that passes phase shifted reference signal R′.
- the high frequency section provides this output to a demodulator 274 in order to recover locating signal frequency f L from the reference signal.
- the locating signal frequency is then fed to a phase shifter 276 .
- the latter is under control of processor 210 via a control line 277 .
- Phase shifter 276 is controlled, depending upon the particular phase shift characteristics of coupling configuration 112 , to provide a phase shift that is essentially equal to the phase shift that is introduced by coupling configuration 112 .
- the output of phase shifter 276 is designated as f L ′ or, in other words, the locating signal frequency with a phase shift that matches the coupling configuration phase shift, so as to be in phase with the locating signal.
- phase shifter 276 can additionally provide compensation for circuitry induced phase shift, if needed, to cause f L ′ to be in phase with the locating signal. It is noted that phase shifter 276 may not be necessary in some implementations, for example, when the locating signal and reference signal are resistively/directly coupled to the cable or associated tracer wire. Alternatively, as will be described below, another embodiment of the transmitter may include phase shift compensation.
- a synchronous detector 278 includes two inputs, one of which receives shifted locating signal frequency f L ′.
- the other input of the synchronous detector is connected to a low frequency section 280 , which is itself connected to antenna cluster 202 via receiver and signal processing section 271 .
- the low frequency section thus provides a band limited output to the other input of synchronous detector 278 which contains locating signal L along with false locating signal L F .
- the synchronous detector provides a strong output responsive to the combination of f L ′ and L, since these two signals are in phase, thereby essentially passing the locating signal on to processor 210 .
- False locating signal L F is rejected since it is, at least approximately, 90 degrees out of phase with shifted locating signal frequency f L ′. That is, the quadrature component of the false locating signal can be rejected by synchronous detection.
- Processor 210 uses the received relative signal strength of the locating signal according to its intended locating procedures. As mentioned above, rejection of the false locating signal is essentially transparent to an operator of the locator.
- the resistance connection between cables 12 ′ and 14 ′ results in false locating signal L F being 180 degrees out of phase with respect to locating signal L, as illustrated. For this reason, if the operator switches from cable 12 to cable 14 during locating, and while at least generally maintaining the orientation of the locator, the signal strength shown on display 206 ( FIG. 5 ) will change signs, thereby notifying the operator that he or she is no longer following cable 12 ′.
- antenna cluster 202 can be used to ascertain an essentially simultaneous signal strength along each of its three orthogonal receiving axes, a total field strength can be determined in the form of a vector sum. Further, antenna 202 ′ can also be used to determine an additional total signal strength at its location, spaced apart from cluster 202 . It is recognized that this configuration is particularly advantageous, since the use of both vector sums reduces orientation requirements with respect to the way in which the operator orients the locator with respect to the cable. More specifically, the vector sum will produce the same value for any orientation of the locator including parallel, perpendicular or otherwise with respect to the cable. The use of a vector sum with respect to one antenna cluster is described in U.S. Pat. No.
- the locating field over the cable is normally assumed to be a circular field with all of the horizontal projections of the fluxlines perpendicular to the cable.
- the upper and lower antennas are used to obtain a ratio of the field strengths at two elevations in order to calculate depth. This ratio is the same, whether using just a portion of the field, with equal misalignment of the antennas, or using the total field strength.
- FIG. 8 another embodiment of a transmitter, that is configured in accordance with the present invention, is generally indicated by the reference number 102 ′.
- transmitter 102 ′ is similar in structure to previously described transmitter 102 .
- the present discussion will be limited to differences between these transmitters.
- One difference resides in the use of a phase shifter 276 ′ in transmitter 102 ′, which eliminates the need for the use of a phase shifter in a receiver which cooperates with transmitter 102 ′.
- the receiver includes a programmable phase shifter, it can be set to introduce zero phase shift.
- a modified coupling arrangement 112 ′ which includes an inductive clamp 300 , a coupling antenna 302 and a direct or resistive clip 304 each of which may be used selectively.
- the inductive clamp is clamped around the cable in a well known manner; coupling antenna 302 is positioned adjacent to the cable onto which it is desired to induce a signal; and clip 304 is attached directly to the cable or tracer wire.
- a switching arrangement 310 is connected between amplifier 152 and each selectable coupling arrangement.
- an inductive configuration such as is provided by clamp 300 and antenna 302 , will introduce a phase shift, while direct clip 304 will not.
- switching arrangement 310 outputs a selection signal to phase shifter 276 ′, as indicated by a dashed line 312 , in a way which causes phase shifter 276 ′ to introduce an appropriate phase shift, based on the particular selection of coupling that is made using switch 310 .
- the latter can be configured in a wide variety of ways in view of this overall disclosure.
- three separate input jacks can be provided, each of which is customized for one type of coupling connection whereby connection to a particular jack produces the appropriate selection signal on line 312 .
- a rotary or push button switch can be provided to electronically select the type of coupling that is in use.
- FIG. 9 illustrates another embodiment of the transmitter of the present invention, generally indicated by the reference number 102 ′′.
- low frequency generator 142 provides locating signal frequency f L directly to amplifier 152 which remains connected to coupling configuration 112 ′.
- the locating signal frequency is also provided to phase shifter 276 ′, which remains responsive to switching arrangement 310 , as described above.
- Phase shifter 276 ′ outputs phase shifted locating signal f L ′ to modulator 144 .
- phase shifter 276 ′ is not required, for example, when a phase shifter is provided in a cooperating receiver.
- Transmitter 102 ′′ also includes an RF generator 320 having an output 322 which provides an RF carrier to modulator 144 .
- modulator 144 generates reference signal R of FIG. 1 .
- the reference signal is coupled to an RF amplifier 324 which drives an RF antenna 330 so as to emanate reference signal R.
- any suitable form of modulation may be utilized.
- an RF carrier is utilized since the reference signal is transmitted through the air to a suitable receiver, yet to be described.
- the present transmitter may utilize any number of commercially available RF transmitters including, for example, spread spectrum 2.5 GHz systems modulated with the reference signal. The principles discussed above remain unchanged with the use of a higher frequency reference signal.
- any suitable transmitter and/or carrier frequency may be employed.
- One variation resides in generating the reference signal with a stable oscillator in the receiver/locator.
- a cooperating transmitter then periodically transmits a synchronization signal such as, for example, a synchronization pulse to lock the internally generated reference signal of the receiver to the reference signal that is in use in the transmitter.
- repeaters can be used to increase the range of the reference signal so long as the phase of the repeated reference signal is maintained or tracked for appropriate phase shifting in the receiver.
- an RF carrier reference signal is advantageous at least for the reason that the RF reference signal, transmitted through the air, is immune to higher attenuation rates which inground reference signals may encounter, even though the carrier frequency for the inground reference signal can be significantly lower that the carrier frequency of an RF reference signal.
- This feature is advantageous with respect to long cables wherein an inground reference signal may become too weak to use, while the locating signal, being at a significantly lower frequency, remains strong.
- receiver 104 ′′ is configured for use with a transmitter, such as transmitter 102 ′′ of FIG. 9 , having provisions for transmitting reference signal R above ground using an RF carrier so as to extend the transmission range to a distance that can be longer than the useful transmission range of the locating signal transmitted through the ground. Since receiver 104 ′′ includes a number of components that are used in receiver 104 of FIG. 7 , descriptions of these components will not be repeated for purposes of brevity.
- Receiver 104 ′′ includes telemetry arrangement 212 in the form of an RF receiver that is connected to RF antenna 214 (see also FIG. 5 ) for receiving reference signal R.
- RF receiver 212 is, in turn, connected to demodulator 274 . Having recovered reference signal R, receiver 104 ′′ operates in essentially the same manner as receiver 104 of FIG. 7 .
- transmitter 102 ′′ is used to induce the locating signal frequency onto cable 12 while transmitting reference signal R through the air for reception by receiver 104 ′.
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Abstract
Description
Claims (13)
Priority Applications (1)
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US17/157,106 US11906685B2 (en) | 2005-04-13 | 2021-01-25 | Distinguishing false signals in cable locating |
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US11/105,804 US7151375B2 (en) | 2005-04-13 | 2005-04-13 | Distinguishing false signals in cable locating |
US11/557,432 US7397249B2 (en) | 2005-04-13 | 2006-11-07 | Apparatus for distinguishing false signals in cable locating |
US12/137,424 US7586308B2 (en) | 2005-04-13 | 2008-06-11 | Phase shifted locating signal as compensation for a coupling configuration phase shift in discriminating a false locating signal |
US12/512,853 US7884610B2 (en) | 2005-04-13 | 2009-07-30 | Distinguishing false signals in cable locating |
US12/979,793 US8080998B2 (en) | 2005-04-13 | 2010-12-28 | Distinguishing false signals in cable locating using a reference signal |
US13/301,487 US8698501B2 (en) | 2005-04-13 | 2011-11-21 | Method for distinguishing a locating signal from a false locating signal |
US14/231,603 US9335431B2 (en) | 2005-04-13 | 2014-03-31 | Distinguishing false signals in cable locating based on a modulated reference signal |
US15/130,840 US9804287B2 (en) | 2005-04-13 | 2016-04-15 | Transmitter for emitting reference signal to distinguish false signals in cable locating |
US15/785,986 US10101487B2 (en) | 2005-04-13 | 2017-10-17 | Transmitter with locating signal frequency phase shift based on switchable cable coupling |
US16/132,361 US10901106B2 (en) | 2005-04-13 | 2018-09-15 | Distinguishing false signals in cable locating |
US17/157,106 US11906685B2 (en) | 2005-04-13 | 2021-01-25 | Distinguishing false signals in cable locating |
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US12/137,424 Expired - Fee Related US7586308B2 (en) | 2005-04-13 | 2008-06-11 | Phase shifted locating signal as compensation for a coupling configuration phase shift in discriminating a false locating signal |
US12/512,853 Expired - Fee Related US7884610B2 (en) | 2005-04-13 | 2009-07-30 | Distinguishing false signals in cable locating |
US12/979,793 Expired - Fee Related US8080998B2 (en) | 2005-04-13 | 2010-12-28 | Distinguishing false signals in cable locating using a reference signal |
US13/301,487 Active 2025-11-16 US8698501B2 (en) | 2005-04-13 | 2011-11-21 | Method for distinguishing a locating signal from a false locating signal |
US14/231,603 Expired - Fee Related US9335431B2 (en) | 2005-04-13 | 2014-03-31 | Distinguishing false signals in cable locating based on a modulated reference signal |
US15/130,840 Active US9804287B2 (en) | 2005-04-13 | 2016-04-15 | Transmitter for emitting reference signal to distinguish false signals in cable locating |
US15/785,986 Active US10101487B2 (en) | 2005-04-13 | 2017-10-17 | Transmitter with locating signal frequency phase shift based on switchable cable coupling |
US16/132,361 Active 2025-04-21 US10901106B2 (en) | 2005-04-13 | 2018-09-15 | Distinguishing false signals in cable locating |
US17/157,106 Active 2025-08-25 US11906685B2 (en) | 2005-04-13 | 2021-01-25 | Distinguishing false signals in cable locating |
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US11/105,804 Active 2025-04-25 US7151375B2 (en) | 2005-04-13 | 2005-04-13 | Distinguishing false signals in cable locating |
US11/557,432 Active US7397249B2 (en) | 2005-04-13 | 2006-11-07 | Apparatus for distinguishing false signals in cable locating |
US12/137,424 Expired - Fee Related US7586308B2 (en) | 2005-04-13 | 2008-06-11 | Phase shifted locating signal as compensation for a coupling configuration phase shift in discriminating a false locating signal |
US12/512,853 Expired - Fee Related US7884610B2 (en) | 2005-04-13 | 2009-07-30 | Distinguishing false signals in cable locating |
US12/979,793 Expired - Fee Related US8080998B2 (en) | 2005-04-13 | 2010-12-28 | Distinguishing false signals in cable locating using a reference signal |
US13/301,487 Active 2025-11-16 US8698501B2 (en) | 2005-04-13 | 2011-11-21 | Method for distinguishing a locating signal from a false locating signal |
US14/231,603 Expired - Fee Related US9335431B2 (en) | 2005-04-13 | 2014-03-31 | Distinguishing false signals in cable locating based on a modulated reference signal |
US15/130,840 Active US9804287B2 (en) | 2005-04-13 | 2016-04-15 | Transmitter for emitting reference signal to distinguish false signals in cable locating |
US15/785,986 Active US10101487B2 (en) | 2005-04-13 | 2017-10-17 | Transmitter with locating signal frequency phase shift based on switchable cable coupling |
US16/132,361 Active 2025-04-21 US10901106B2 (en) | 2005-04-13 | 2018-09-15 | Distinguishing false signals in cable locating |
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US8069175B2 (en) | 2002-04-10 | 2011-11-29 | Google Inc. | Delegating authority to evaluate content |
US7151375B2 (en) | 2005-04-13 | 2006-12-19 | Marlin Technology, Inc. | Distinguishing false signals in cable locating |
US8264226B1 (en) * | 2006-07-06 | 2012-09-11 | Seektech, Inc. | System and method for locating buried pipes and cables with a man portable locator and a transmitter in a mesh network |
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US7884610B2 (en) | 2011-02-08 |
US20080246482A1 (en) | 2008-10-09 |
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US7586308B2 (en) | 2009-09-08 |
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US20090289634A1 (en) | 2009-11-26 |
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US8698501B2 (en) | 2014-04-15 |
US20180038982A1 (en) | 2018-02-08 |
US20060232258A1 (en) | 2006-10-19 |
US20210247539A1 (en) | 2021-08-12 |
US20140210477A1 (en) | 2014-07-31 |
US10901106B2 (en) | 2021-01-26 |
US9335431B2 (en) | 2016-05-10 |
US20120062234A1 (en) | 2012-03-15 |
US20190033480A1 (en) | 2019-01-31 |
US7397249B2 (en) | 2008-07-08 |
US20160231447A1 (en) | 2016-08-11 |
US8080998B2 (en) | 2011-12-20 |
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